Preparation of 2-chlorobutene-2



, droxide.

Patented. July PATENT OFFICE 2,291,375 PREPARATION OF Z-CHLOROBUTENE-ZOliver W. Cass, Niagara Falls, N. Y., assignor to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application April 26, 1940, Serial No. 331,887

12 cla ms. (01. 260-654) This invention relates to the preparation of2-chlorobutene-2 and particularly to the preparation of this compound bythe dehydrochlorination of 2,3-dichlorobutane.

2-Chlorobutene-2 has been prepared from 2,3- 5 dichlorobutane by themethod of British Patent 332,605 (1930) which involves treatment of thelatter compound with alcoholic potassium hy- That method requires theues of relatively costly material, one of which is highly inflammable.Other disadvantages thereof which make the method unattractive forcommercial application are that it is difficult to separate the reactionproduct from the alcohol and that the presence in the reaction mixtureof alcohol results in the formation of by-product ether compounds.

It is an object of the present invention to provide an improved methodof preparing 2-chlorobutene-2 from 2,3-dichlorobutane. A further objectis the provision of a practical method for carrying out thedehydrochlorination of 2,3-dichlorobutane using an alkaline agentin anaqueous medium, whereby good yields of 2-chlorobutane-2 may be obtained.These and still further objects will be apparent from the-ensuingdescription of the invention.

The above objects may be accomplished in accordance with my inventionbysubjecting 2,3-dichlorobutane to the action of an alkaline agentselected from the group consisting of alkali metal hydroxides, alkalineearth metal hydroxides, and mixtures of alkali metal and alkaline earthmetal hydroxides, in an aqueous medium at a temperature within the rangeof 118 to 250 C. By means of my improved method, yields of pure2-chlorobutene-Z of the order of 90% may be readily obtained. The methodis easily carried out and is practicable for commercial operations.

The use of aqueous solutions of strong alkali, such as sodium hydroxide,in preparing vinyl chloride and isopropenyl chloride from ethylenedichloride and propylene dichloride, respectively, is described by Youngin U. S. Patent 1,752,049.

. That patent, which does not mention the treatment of four-carbonolefine dichlorides, states that the treatment of propylene dichloridewith an alcoholic solution of potassium hydroxide yields propenylchloride, whereas isopropenyl chloride is produced when the samematerial is treated with aqueous caustic at elevated temperature. Fromthat disclosure it is apparent that the monochloro olefine product orproducts obtainable from a particular olefine dichloride bydehydrochlorination reactions with alkaline agents is or are notpredictable. This is particularly true in the case of 2,3-dichlorobutanefrom which two monochlorobutenes, namely 2-chlorobutane-2 and3-chlorobutene-l, are theoretically possible, and it could not have beenpredicted that the former compound could be obtained in substantiallyquantitative yields from 2,3-dichlorobutane by practicing the presentmethod. Indeed, it is surprising and entirely unexpected that2-chlorobutene-2 could be obtained in such good yields from 2,3-dichlorobutane by the present method in view of German Patent 246,572,which describes the preparation of 2,3-dihydroxybutane from the samedichlorobutane by treatment with aqueous calcium hydroxide at C.

Particularly good results may be obtained by the present method when analkali metal hydroxide, such as sodium hydroxide, is employed as the.alkaline agent, by effecting the reaction at a temperature withinv therange 118 to 210 C. Operation within the range of to C. is particularlyrecommended. When using an alkaline earth metal hydroxide, such as lime,as the alkaline agent, operation at a temperature within the range of150 to 250 C., .and preferably to 220 C., is effective. Thesetemperature ranges may be varied somewhat depending upon the particularalkaline material used and also upon the concentration of the agent inthe aqueous medium.

The concentration of the alkaline agent in the aqueous medium may bevaried over a wide range. Concentrations within the range of 10 to 30%and preferably 15 to 25% give especially good results, althoughconcentrations outside of these ranges may be employed. The amountofalkali used may also be varied considerably, but inorder to eifect ascomplete. conversion as possible an excess of at least 5% over thatamount theoretically required to convert the 2,3-dichlorobutane to2-chlorobutene-2 should be used.

Inorder that the reaction may be carried out at the elevatedtemperatures indicated above, it will of course be necessary that thereaction mixture be maintained under suitable pressure during the courseof the reaction. This may be conveniently done by effecting the reactionin a closed vessel, such as an autoclave or any of the usual bomb-typereactors.

I have discovered that best results are obtained when 2-chlorobutene-2is removed from the reaction mixture as it is produced therein. This maybe conveniently accomplished by equipping the reactor with a suitablestripping column which functions to condense and return to the reactionmixture unconverted 2,3-dichlorobutane while permitting 2-chlorobutene-2to escape in the vapor form. The vapors of 2-chlorobutene-2 are passedfrom the stripping column to a condenser where "they=;; are of crudeproduct; which may be purified byusual distillation methods to separateunconverted 2,3-dichlorobutane not returned to the reactor by thestripping column.

The invention is further illustrated by the'following examples.

Example 1 I 10 gram-moles of 2,3-dichlorobutene and 11.2 gram-moles ofsodium hydroxide in the form of a 25% Example 2 20 gram-moles of2,3-dichlorobutane and 22.4 gram-moles of sodium hydroxide in the formof a 25% aqueous solution were charged into a reaction bomb as describedin Example 1. The contents of the bomb were heated to a temperature of135 to 140 C. for a period of 2% hours, after which 2-chlorobutene-2 wasisolated from the reaction mixture in an amount corresponding to a yieldof 82.6% based upon the amount of dichlorobutane consumed. Of thedichlorobutane, initially charged 52.2% was converted to themonochlorobutene.

Example 3 40 pounds of 2,3-dichlorobutane of 90% purity and'75 pounds ofa 20% sodium hydroxide solution ,were charged into a horizontal30-gallon autoclave, 15 inches with a paddle-type agitator operating at80 R. P. M. The autoclave was also provided with a stripping column 15feet long and 3 inches wide which was packed for 10 feet with inchRaschig rings. This column was equipped with .a bayonet-type refluxcondenser in the top feet of the column. Heat was applied to theautoclave so as to maintain a temperature in the re-v actor in theneighborhood of 150 to 160 C. During the reaction period cooling waterwas applied to the condenser in the stripping column so as to maintain aset reflux calculatedto be about 20 pounds per hour. The vapor draw-offvalve from the stripping column was adjusted so that product was removedfrom the reactor at the rate of about 4 pounds per hour. The reactionwas stopped when the density of the distillate rose to 1.0, indicatingthat the material coming over then was substantially all water. Byoperation in this manner 26.2 pounds of crude product was obtained fromwhich 22.1 pounds of pure product was recovered by usual distillationmethods. The yield of purified product was 87.8% of condensed in theform may be used as such or :was found the theoretical based upon thedichlorobutane employed.

Example 4 4 gram-moles of 2,3-dichlorobutane and 800 grams of a limeslurry containing 2.2 gram moles of' calcium hydroxide were charged intoa shaker bomb as 'in' the method of .Example 1.

The bomb and its contents were shaken for 6 hours, during which time thereaction mixture was maintained at a temperature of approximately 150 C.At the conclusion of the run it that 14% of, the dichlorobutane chargedinto the bomb was converted to 2- aqueous solution were charged into apressure bomb which was provided with means I. D. by 3% ft. lon providedkaline earth metal hydroxides in an aqueous mevchlorobutene-2, the yieldof the latter compound theoreticalbased upon the being 89% of the amountof the dichloride not recovered as such.

Example 5 An experiment similar to that described in Example 4 wascarried out at a temperature of 200 C. At the end of 6 hours 57% of thedichlorobutane charged had been converted to give a yield of 82.5% of2-chlorobutene-2 based upon the amount of dichlorobutane not recoveredas such.

It has been discovered that the rate of conversion when using lime asthe alkaline material may be increased considerably by having present inthe reaction medium a substantial amount of sodium hydroxide. Thus, inexperiments carried out substantially as described in Examples 4 and 5except that a temperature of C. was employed, the rate of conversion wasincreased. ap

proximately 50% by substituting 0.4 mole of sodium hydroxide for ide. Ingeneral the use of 0.01 to 0.5 mole of sodium hydroxide per mole ofcalcium hydroxide is sufiicient to increase substantially the reactivityof the latter. The proportions of the two agents may be varied so thatsodium hydroxide predominates, but due to the relative cheapness oflime, the use of a mixture consisting chiefly of calcium hydroxide, butcontaining suflicint sodium hydroxideto increase substantially thereactivity of the former, is prefe'rred.

One of the chief advantages of the present improved method is that cheapalkaline materials may be used. No costly inflammable solvent isrequired and an easy separation of the desired product is secured. Themethod may be practiced to give yields of 2-chlorobutene-2 approachintheoretical values and in general the compound may be obtained assubstantially the sole organic reaction product.

Many widely different embodiments of the invention may be practicedwithout departing from the scope and spirit thereof. Accordingly, itnotintended that the invention be limited to the specific embodiments anddescriptions thereof set forth above, except as indicated in theappended claims.

I claim: 1. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with an alkaline material selected from the groupconsisting of alkaline earth metal hydroxides, alkali metal hydroxides,and mixtures of alkali and. al kaline earth metal hydroxides in anaqueous medium at a temperature of 118 to 250 C.

2. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with an alkaline material selected from the groupconsisting of alkaline earth'metal hydroxides, alkali metal hydroxides,and mixtures of alkali and aldium at a temperature of 118 to 250 C. andwith- 0.2 mole of calcium hydroxdrawing 2-chlorobutene-2 from. thereaction mixture as it is formed.

3. The method of claim 1 using an aqueous medium containing the alkalinematerial in a concentration of 10 to 30% by weight.

4. The method of claim 1 using an aqueous medium containing atleast aexcess of the alkaline material in a concentration of to by weight.

5. A method of preparing 2-chlorobutene-2 sodium hydroxide solution of10 to 30% concentration by weight at to C.

9. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with calcomprising reacting 2,3-dichlorobutane withsodium hydroxide in the form of an aqueous solution at a temperature of118 to 210 C.

6. A method of preparing 2-chlorobutene-2 I comprising reacting2,3-dichlorobutane with sodium hydroxide in the form of an aqueoussolution at a temperature of 130 to 160 C.

7. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with a sodium hydroxide solution of 10 to 30%concentration by weight at 118 to 210 C.

8. A method of preparing 2-ch1orobutene-2 comprising reacting2,3-dichlorobutane with a cium hydroxide in an aqueous medium at 150 to250 C.

10. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with a 10 to 30% aqueous slurry of calcium hydroxideat to 220 C. a

11. A method of preparing 2-chlorobutene-2 comprising reacting2,3-dichlorobutane with an sodium hydroxide per mole' of calciumhydroxide present therein at a temperature of 118 to 250 C.

OLIVER w. CASS.

